Lube basestocks are commonly used for the production of lubricants, such as lubricating oils for automobiles, industrial lubricants and lubricating greases. They are also used as process oils, white oils, metal working oils and heat transfer fluids. Finished lubricants consist of two general components, lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
According to the American Petroleum Institute (API) classifications, lube basestocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base oils are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III basestocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base oils can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources. Group IV basestocks, the poly (alpha olefins) (PAO), are produced by oligomerization of alpha olefins, such as 1-decene. Group V base oils include everything that does not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG) and esters.
TABLE 1API classificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≧90≧90PolyAll others% S>0.03≦0.03≦0.03alpha-notViscosity80-12080-120≧120olefinsbelongingIndex (VI)(PAO)toGroup I-IV
Natural oils derived from biological sources are sometimes used as lubricants, but to a small scale, due to their poor low-temperature properties and hydrolysis instability. The triglyceride esters in natural oils are often hydrolyzed to yield fatty acids, which can be subsequently converted into esters as synthetic lubricants.
For environmental, economical, and regulatory reasons, it is of interest to produce fuels, chemicals, and lube oils from renewable sources of biological origin. So far only esters of renewable and biological origin have been used in applications such as refrigeration compressor lubricants, bio-hydraulic oils and metal working oils. In automotive and industrial lubricants, esters from biological sources are used in very small fractions as additives due to technical problems as well as their high prices. For example, ester base oils can hydrolyze readily producing acids, which in turn cause corrosion on lubricating systems.
In contrast, lube basestocks consisting of hydrocarbons from biological sources do not have those technical problems associated with esters from same sources. Most common biological sources for hydrocarbons are natural oils, which can be derived from plant sources such as canola oil, castor oil, sunflower seed oil, rapeseed oil, peanut oil, soy bean oil, and tall oil, or derived from animal fats. The basic structural unit of natural oils and fats is a triglyceride, which is an ester of glycerol with three fatty acid molecules having the structure below:

wherein R1, R2, and R3 represent C4-C30 hydrocarbon chains. Fatty acids are carboxylic acids containing long linear hydrocarbon chains. Lengths of the hydrocarbon chains most commonly are 18 carbons (C18). C18 fatty acids are typically bonded to the middle hydroxyl group of glycerol. Typical carbon numbers of the fatty acids linked to the two other hydroxyl groups are even numbers, being between C14 and C22.
In the field of fuels, so-called renewable source components are now required both in the US and Europe. Although there is no imminent requirement for lube products currently, generating premium basestocks from renewable sources on a large scale is attractive for the same policy reasons that led to the imposition of regulations in the higher volume fuel area. In fact, with recent advances in biofuels, natural oils are becoming increasingly available as feedstocks that provide fuel value comparable to that of petroleum oils. Converting these bio-feeds to lubes can give significant value uplift.
Kolbe reaction is one of the oldest and best-known electro-organic reactions and is defined as one-electron oxidation of carboxylate ions RCOO— with decarboxylation that leads to a radical R.. These radicals can dimerize to form a larger molecule R—R (Kolbe coupling). The overall reaction is summarized as follows:
Weiper-Idelmann et al, Acta Chemica Scandinavica 52 (1998) pp. 672-682 report dimerization of fatty acids having long chain hydrocarbons by Kolbe electro-coupling. Cross-coupling can also occur in the co-electrolysis of two different acids.
U.S. Pat. No. 7,582,777 to Bloom (issued on Sep. 1, 2009) describes a method for producing long chain (C22-C50) polyunsaturated hydrocarbons via electro-coupling of C12-C26 fatty acids.
However, it is known that Kolbe electrochemical coupling is unsuccessful when an arylic acid is used (see Jerry March, Advanced Organic Chemistry—Reactions, Mechanisms and Structure, fourth edition, John Wiley & Sons, Inc. 4th Ed. (1992), pp. 729-730).
It is surprisingly found that, by proper choice of solvents, bases, and a fatty acid to arylic acid ratio, homo-coupling of arylic acids such as phenylacetic acid and cross-coupling of arylic acids with fatty acids are feasible electrochemically.